Egypt bombed Islamic State militants in neighboring Libya on Monday and called on the United States and Europe to join an international military intervention in the chaotic North African state after extremists beheaded a group of Egyptian Christians.

The airstrikes bring Egypt overtly into Libya's turmoil, a reflection of Cairo's increasing alarm. Egypt now faces threats on two fronts — a growing stronghold of radicals on its western border and a militant insurgency of Islamic State allies on its eastern flank in the Sinai Peninsula — as well as its own internal challenges.

Islamic State group weapons caches and training camps were targeted "to avenge the bloodshed and to seek retribution from the killers," a military statement said. "Let those far and near know that Egyptians have a shield to protect and safeguard the security of the country and a sword that cuts off terrorism."

The announcement on state radio represents Egypt's first public acknowledgement of military action in post-Moammar Gadhafi Libya, where there has been almost no government control.

Libya is where the Islamic State group has built up its strongest presence outside Syria and Iraq. Egyptian President Abdel-Fattah el-Sissi is lobbying Europe and the United States for a coordinated international response similar to the coalition air campaign in those countries.

"What is happening in Libya is a threat to international peace and security," said El-Sissi.

El-Sissi spoke with France's president and Italy's prime minister Monday about Libya, and sent his foreign minister, Sameh Shukri, to New York to consult at the United Nations ahead of a terrorism conference opening Wednesday in Washington.

Photos of the fight against Islamic State

The bombs were dropped by U.S.-made F-16 fighter jets that left Egyptian bases for targets in the eastern Libyan city of Darna, according to Egyptian and Libyan security officials who spoke on condition of anonymity because they were not authorized to talk the press.

The strikes came hours after the Islamic State group issued a grisly video of the beheadings of 21 Egyptian Christians, mainly young men from impoverished families who were kidnapped after travelling to Libya for work. The video shows them being marched onto what is purported to be a Libyan beach before masked militants with knives carve off their heads.

Thirteen of the 21 came from Egypt's tiny Christian-majority village of el-Aour, where relatives wept in church and shouted the names of the dead on Monday.

Babawi Walham, his eyes swollen from crying and barely able to speak, said his brother Samuel, a 30-year-old plumber, was in the video his family saw on the news Sunday night.

"Our life has been turned upside down," he told The Associated Press. "I watched the video. I saw my brother. My heart stopped beating. I felt what he felt."

Hassan Ammar, AP

Family members of one of the abducted Coptic Christians that were reportedly slain by Islamic State militants in a new video.

Family members of one of the abducted Coptic Christians that were reportedly slain by Islamic State militants in a new video. (Hassan Ammar, AP)

Libyan extremists loyal to the Islamic State and some 400 fighters from Yemen and Tunisia have seized control of Darna and the central city of Sirte and have built up a powerful presence in the capital, Tripoli, as well as the second-largest city, Benghazi. Libya's internationally recognized government has been driven into the country's far eastern corner.

Without publicly acknowledging it, Egypt and the United Arab Emirates carried out airstrikes against Islamist-allied militias last year, according to U.S. officials.

"We will not fight there on the ground on behalf of anyone, but we will not allow the danger to come any closer to us," said one Egyptian security official, who claimed that intelligence recently gathered in Libya suggests advanced preparations by Islamic State militants to cross the border into Egypt. He did not elaborate.

For now, any foreign intervention should be limited to air strikes, with political and material support from the U.S.-led coalition staging airstrikes in Iraq and Syria, the Egyptian official said. Egypt already has been amassing intelligence on extremists in Libya in a joint effort with the Libyan armed forces and West European nations, including France.

Insurgents in Egypt's strategic Sinai Peninsula who recently declared their allegiance to the Islamic State rely heavily on arms smuggled from Libya, which has slid into chaos since the 2011 uprising that toppled Gadhafi's 41-year rule.

France, a lead player in the campaign to oust Gadhafi, has campaigned for months for some kind of international action in Libya, and announced a deal Monday to sell fighter jets to Egypt. French troops are already in place near Libya's southern border in Niger as part of a counterterrorism force.

French President Francois Hollande's office said he and al-Sissi both "stressed the importance that the Security Council meets and that the international community takes new measures to confront this danger."

Italian Defense Minister Roberta Pinotti, meanwhile, said in an interview published Sunday in the Il Messaggero daily that her country is ready "for geographic, economic and historic reasons" to lead a coalition of European and North African countries to stop the militants' advance in a country less than 500 miles from Italy's southern tip.

"If in Afghanistan we sent 5,000 men, in a country like Libya which is much closer to home, and where the risk of deterioration is much more worrisome for Italy, our mission and commitment could be significant, even numerically," she was quoted as saying.

A NATO official who spoke on condition of anonymity in keeping with NATO practice said "there is no discussion within NATO on taking military action in Libya."

However, Allies consult regularly on security developments in North Africa and the Middle East and we follow events in the region closely," the official said. "We also stand ready to support Libya with advice on defense and security institutions-building."